1. Field of the Invention
The present invention relates to a system for preparing a consolidating medium which is injected into the ground to provide consolidation or water cut-off of the ground, or a material for such consolidating medium (which will be generally referred to as a ground impregnating material), and more particularly, to a system for producing a ground impregnating material, in which controlling of the absolute flow rate of a pressurized carbon dioxide gas is simplified, and carbon dioxide is permitted to join a base component of the ground impregnating material at a given ratio within a range of acceptable ground pressures.
2. Description of the Prior Art
There has been proposed a medium injection process for injecting a consolidating medium consisting essentially of a water glass (sodium silicate) and carbon dioxide gas serving as a hardening agent into a weak or water-leaked ground to provide consolidation or water cut-off of the ground.
In general, in injecting an aqueous sodium silicate solution and carbon dioxide gas into the ground in a joining manner, uniform aggregates of sodium silicate will not be formed unless carbon dioxide gas to be mixed is supplied at a substantially constant proportion in absolute quantity to the aqueous sodium silicate solution. This reason is as follows: If the pressure within the ground varies, the amount of carbon dioxide gas injected varies significantly, resulting in a failure to maintain a constant ratio to the sodium silicate, causing non-uniformity of a colloid material produced from the reaction of the sodium silicate and carbon dioxide gas. Consequently, a uniform aggregate is not provided.
For example, if the injection rate of the consolidating material into the ground is kept constant, the injection pressure normally varies from zero to about 20 kg/cm.sup.2. On the contrary, the absolute amount of the aqueous sodium silicate solution would not vary even if the injection pressure varies, because the aqueous sodium silicate solution is liquid. However, carbon dioxide gas varies in volume and also in absolute amount due to the variation of injection pressure.
For one of the approaches to the above problems, there has been proposed a medium injection system as described in Japanese Patent Publication No. 42769/84. This proposed system comprises an injection pipe inserted into the ground, a sodium silicate storage tank connected to the interior of the injection pipe, and a carbon dioxide bomb connected to the interior of the injection pipe, wherein a pressure variation sensor is interposed between the carbon dioxide bomb and the injection pipe, the pressure variation senser being constituted of an automatic flow rate adjuster valve, a flow meter connected via a differential pressure transmitter and an opening and closing operator to a flow rate indication adjuster, and a pressure transmitting unit similarly connected via a graphic operator to the flow rate indication adjuster, these three components being connected sequentially between the injection pipe and the carbon dioxide gas bomb, so that the absolute flow rate of carbon dioxide gas is controlled by the automatic flow rate adjuster valve being operated by the flow rate indication adjuster on the basis of the results of calculation in both of the operators, thereby injecting the aqueous sodium silicate solution and the carbon dioxide gas in a joining manner at a constant ratio of their absolute flow rates.
The above prior art injection system can provide an advantage that the provision of the pressure variation sensor between the carbon dioxide bomb and the injection pipe makes it possible to inject the aqueous sodium silicate solution and carbon dioxide gas into a ground in the joining manner at a constant ratio of their absolute flow rates, irrespective of a variation in ground pressure (kg/cm.sup.2). In practice with this system, however, there is a necessity for a complicated control system for sensing a pressurized carbon dioxide gas in an amount to correspond to the ground pressure, resulting in an increased cost of equipment for the control system, and also providing practical problems of requirements for checks in performance, control and maintenance of individual control elements as well as careful control of operation.